Hexarelin is a small synthetic peptide that tells the brain to release a pulse of growth hormone. It belongs to the GHRP family — the "growth-hormone-releasing peptides" — and in early human studies it was one of the most potent of them at doing that job1. What makes it unusual is a second job: it also latches onto a receptor called CD36 that sits on heart-muscle cells, which is why much of its recent research has drifted away from muscle-building and toward the heart2.
In plain terms: a strong "release growth hormone" signal that, unlike its cousins, also talks directly to the heart.
What it is
Hexarelin is a chain of six amino acids (the building blocks of proteins), which is why its class name is a "hexapeptide" — hexa meaning six. It was developed in the 1990s as a synthetic analog of an earlier peptide, GHRP-6, engineered to be more stable and more potent1.
It is a secretagogue, a word worth unpacking: a secretagogue is something that makes a gland secrete, or release, its own hormone. So hexarelin does not add growth hormone to the body. It pushes the pituitary — a pea-sized gland under the brain — to release the growth hormone it already makes.
How it works — two receptors, not one
Most GHRP-family peptides act through a single doorway: the growth-hormone-secretagogue receptor, or GHS-R1a. This is the same receptor the hunger hormone ghrelin uses, which is why these peptides are sometimes called ghrelin mimics. When hexarelin activates GHS-R1a in the pituitary and hypothalamus, the pituitary releases a burst of growth hormone1.
Hexarelin's distinctive trait is a second receptor: CD36. CD36 is a scavenger receptor — a molecule on the cell surface that binds a wide range of partners — and it is present on heart-muscle cells and small blood-vessel cells. Researchers labelled hexarelin with a tracer and found it bound CD36 in cardiac tissue, and that this binding, not growth hormone, drove its effects on the heart2.
In plain terms: one receptor makes growth hormone come out; the other is a direct line to the heart.
Pharmacokinetics — how it is taken up and how long it lasts
The most useful human numbers come from a 1994 study that gave hexarelin by four different routes to twelve healthy volunteers and measured the growth-hormone response1. It is a good example of why route matters:
| Route studied | Relative bioavailability | Note |
|---|---|---|
| Under the skin (subcutaneous) | ~77% | The most efficient injected route in the study |
| Into the nose (intranasal) | ~5% | Much weaker uptake |
| By mouth (oral) | ~0.3% | Almost none survives digestion |
Bioavailability means the fraction of a dose that actually reaches the bloodstream in active form. The lesson from the table: hexarelin is a peptide, and peptides are largely destroyed by the gut, so swallowing it wastes almost all of it1. The growth-hormone pulse it produces is also short-lived — it comes on within minutes and fades within a couple of hours, so its action is a spike, not a steady background level.
What the studies actually found
Hexarelin has two separate evidence stories, and it is important to keep them apart. The growth-hormone story has genuine human data. The heart story is compelling but almost entirely from animals. Note the model in each row:
| Study | Model / level | Key result | Year |
|---|---|---|---|
| Ghigo et al.1 | Human (n=12, healthy) | Strongly released GH; ~77% bioavailability under the skin, near-zero orally | 1994 |
| Bodart et al.2 | Rat heart tissue | Identified CD36 as the cardiac receptor carrying hexarelin's cardiovascular action | 2002 |
| Mao et al. — review3 | Review (animal + mechanism) | Summarised hexarelin's blood-pressure, output, and heart-protection effects beyond GH | 2014 |
| McDonald et al.4 | Mouse (heart attack model) | Preserved heart function and reduced fibrosis (scarring) after a simulated heart attack | 2018 |
The pattern: real human proof that it releases growth hormone, plus a consistent but preclinical signal that it protects heart tissue through CD3634. In the mouse heart-attack study, treated animals kept more pumping function and formed less scar tissue than untreated ones — an animal result, not a human one4.
The cardiac angle — why it is interesting
The heart findings are what set hexarelin apart from other GHRPs. Because CD36 sits on heart cells, hexarelin can act on the heart directly, independent of growth hormone. In animal models this has translated into smaller areas of damage after blocked blood flow (ischaemia) and less remodelling — the unhelpful stiffening and scarring a heart undergoes after injury3. Reviews describe effects on the pro-survival signalling pathways cells use to resist dying2.
In plain terms: in animals it behaves like a "protect the heart cells" signal. That is a strong lead — and still only a lead, because the confirming human trials have not been done.
Honest limitations
Three caveats keep this in proportion. First, the exciting cardiac results are animal studies; a rat or mouse heart is not a human heart, and the leap from one to the other fails more often than it succeeds. Second, hexarelin's growth-hormone effect can fade with repeated exposure — studies describe desensitisation, where the pituitary responds less over time. Third, hexarelin is not an approved medicine; it is a research compound with no regulatory sign-off for any use. This page explains what it is and what studies used, takes no position on sourcing, and is not medical advice.
Latest research
- The 1994 human study remains the anchor for hexarelin's growth-hormone effect and the practical fact that it works injected but not swallowed1.
- The heart story has grown, from the 2002 identification of CD36 as its cardiac receptor2 to a 2018 mouse heart-attack study showing preserved function and less scarring4. The 2014 review pulls this together3.
- The gap is unchanged: no controlled human trials confirm the cardiac benefits. Until those exist, the heart-protection idea stays in the promising-but-unproven column. We update this section as new work appears.
The short version
Hexarelin is a potent GHRP-family peptide that makes the pituitary release growth hormone — proven in humans — and also binds CD36 on heart cells, which is why its recent research focuses on the heart. The cardiac and heart-protection findings are almost all from rats and mice. It is a research compound, not a medicine. Educational overview only. For related peptides, see ipamorelin and CJC-1295.